Field of the Invention
The present invention relates generally to the construction and configuration of a rotor for electrical machines including both motors and generators, and more particularly to an improved two pole rotor construction with the entire portion of the rotor between two end pieces being a diametrically magnetized solid clyindrical two pole magnet, which construction provides the maximum possible magnetomotive force for a given permanent magnet rotor size, thereby allowing a larger magnetic air gap than found in machines having conventional rotors and also facilitating the use of toothless stator construction.
In the design and construction of permanent magnet machines, there are two considerations which dictate the design of an improved permanent magnet machine having great appeal to potential purchaser. These two factors are, first, the desire to minimize the cost of the machine, or to provide the most machine for the least money, and secondly to increase machine efficiency while reducing machine size by utilizing the ever-increasing high energy product permanent magnets.
With regard to the first of these factors, the desire to minimize construction cost of a permanent magnet machine, it is highly desirable to utilize a toothless stator construction such as that taught in Assignee's concurrently filed U.S. patent application Ser. No. 800,184, entitled "Toothless Stator Construction for Electrical Machines", which patent application is hereby incorporated herein by reference. The use of a toothless stator construction necessarily requires that the magnetic air gap is considerably larger than that generally encountered in existing machines, so it is necessary that the permanent magnet rotor provide the maximum possible magnetomotive force to make practical a machine with such a large magnetic air gap. A second consideration with regard to minimizing construction cost of a permanent magnet machine is that the rotor assembly have the minimum possible number of parts, thereby reducing both labor and part cost as much as possible.
Typical state-of-the-art rotor construction utilizes a minimum of four individual precision machined magnets, a precision machined ferro-magnetic support yoke, and an aluminum cage consisting of spacers and rings and used to position and support the individual magnets. Construction of such conventional permanent magnet rotors typically includes at least 12 individual parts contained in the rotor, each of which must be precision machined to result in proper mechanical fit of the various parts. It may be appreciated that the high parts count and precision machining requirements result in relatively expensive rotor fabrication costs.
It is therefore an object of the present invention to reduce both the number of parts contained in the rotor and the rotor fabrication time, which is mainly due to precision machining of the various parts contained in the rotor. It may be appreciated that by accomplishing a substantial reduction in the cost of the rotor, while simultaneously utilizing the substantially cheaper toothless stator construction described in the above-referenced copending patent application, the overall construction cost of a permanent magnet machine may be substantially reduced.
The second objective of the present invention is to maximize machine efficiency and provide in a reduced size and weight package a machine having equivalent power and at least equivalent efficiency of a larger conventional machine. In order to reduce the size of the machine without reducing efficiency or output of the machine, it is necessary that the permanent magnet rotor provide the maximum possible magnetomotive force for a given rotor size. By so doing, the rotor of the present invention may be used with the toothless stator construction referenced above to construct a compact, efficient electrical machine having substantially no disadvantages.
It is an objective, therefore, of the present invention to accomplish both a substantial reduction in cost of machine construction, and a substantial reduction in machine size and weight with no reduction in efficiency while providing the same output as a larger machine. It will be appreciated that in accomplishing these objectives, the present construction will provide a highly advantageous rotor construction.